Recognition/anti-collision light for aircraft

ABSTRACT

A recognition light includes a reflector having an axis and first and second annular semi-parabolic reflective surfaces which have respective focal points axially spaced apart from one another, and first and second annular lamps respectively disposed at the focal points. A cover surrounds the reflector and lamps and includes a lens for focusing the light along a plane perpendicular to the axis of the reflector, the lens including first and second Fresnel lens portions each including a convex lens and a prism lens, the convex lenses being disposed adjacent one another and transaxially aligned with the first and second lamps, respectively. A light detector detects light emitted from at least one of the lamps, a monitor circuit provides a fail signal when a characteristic of the light output of at least one of the lamps does not satisfy a specified criteria, and a control circuit first activates the first lamp and then the second lamp in response to receipt of the fail signal of the monitor circuit.

FIELD OF THE INVENTION

[0001] The present invention relates to recognition/anti-collisionlights and, more particularly, to a method and apparatus for extendingthe useful life of such lights and/or for detecting the failure of suchlights.

BACKGROUND OF THE INVENTION

[0002] Recognition/anti-collision lights are used on aircraft to producebright flashes of light readily visible to the human eye for improvingrecognition of the aircraft from the ground or from other aircraft. TheFAA (Federal Aviation Administration) currently mandates that aircrafthave such lights with an acceptable minimum effective light intensity of100 or 400 candela (depending on the aircraft) when viewed within fivedegrees of a horizontal plane.

[0003] Many prior art recognition/anti-collision lights include aflashtube, or strobe light, that initially produces a light intensitythat meets government guidelines. However, the light intensity of theflashtube gradually degrades with use over time and eventually fallsbelow the minimum intensity requirements, thereby requiring servicingand/or replacement of the flashtube. The mean time between failure(MTBF) of a typical flashtube is about 1500-3000 hours.

[0004] Anti-collision lights are therefore periodically tested, in someinstances with elaborate equipment, to ensure that they meet the FAArequirements. A common practice has been to replace the lights on ascheduled basis to ensure proper illumination requirements are met eventhough many of the lights still satisfy illumination requirements.

[0005] In order to reduce the frequency at which arecognition/anti-collision light requires replacement, it would bedesirable to have an anti-collision light with an improved (increased)mean time between failure (MTBF).

SUMMARY OF THE INVENTION

[0006] The present invention provides a recognition/anti-collision lightincluding, in a preferred embodiment, two flashtubes and a controlsystem that sequentially operates the two flashtubes in order to extendthe overall useful life of the light. The invention also provides atechnique for extending the life of a single flashtube or multipleflashtubes.

[0007] According to one aspect of the invention, a recognition lightcomprises a reflector having an axis and first and second annularsemi-parabolic reflective surfaces which have respective focal pointsaxially spaced apart from one another, and first and second annularlamps respectively disposed at the focal points.

[0008] According to another aspect of the invention, a recognition lightcomprises a parabolic reflector, first and second annular lampssurrounding the reflector, and a lens cover surrounding the reflectorand lamps, the lens cover including a lens for focusing the light alonga plane perpendicular to the axis of the reflector, the lens includingfirst and second Fresnel lens portions each including a convex lens anda prism lens, the convex lenses being disposed adjacent one another andtransaxially aligned with the first and second lamps, respectively.

[0009] According to another aspect of the invention, a recognition lightcomprises first and second lamps, a light detector positioned to detectlight emitted from at least one of the lamps, a monitor circuitconnected to the light detector for providing a fail signal when acharacteristic of the light output of at least one of the lamps does notsatisfy a specified criteria, and a control circuit connected to themonitor circuit and the first and second lamps for first activating thefirst lamp and then the second lamp in response to receipt of the failsignal of the monitor circuit.

[0010] According to another aspect of the invention, a recognition lightof an aircraft comprises a flashtube, a light detector positioned todetect light emitted from the flashtube, a monitor circuit connected tothe light detector for measuring the intensity of the detected light andcomparing the measured intensity with a reference value corresponding toa predetermined light intensity level, and a control circuit connectedto the flashtube and monitor circuit for flashing the flashtube at afirst power level and then at an increased power level when the measuredintensity drops below the reference value, thereby to increase theintensity of the flashes emitted by the flashtube to above thepredetermined light intensity level.

[0011] According to another aspect of the invention, a method forincreasing the useful life of a recognition light of an aircraftcomprises flashing a flashtube, monitoring the light output of theflashtube, comparing the measured light output of the flashtube with areference value corresponding to a predetermined light intensity value,increasing the power delivered to the flashtube when the measured lightoutput drops below the reference value, thereby to increase theintensity of the flashes emitted by the flashtube to above the referencevalue.

[0012] According to a further aspect of the invention, a method formonitoring the useful life of an aircraft recognition light comprisesflashing a flashtube, and monitoring the light output of the flashtubewith a light detector that converts the detected light output into anintegrated output voltage corresponding to the light output of aplurality of flashes of the flashtube.

[0013] According to another aspect of the invention, a method forincreasing the useful life of a recognition light comprises providingfirst and second lamps, operating the first lamp, monitoring acharacteristic of the light output of the first lamp and providing afail signal when the characteristic of the light output of the firstlamp does not satisfy a specified criteria, and stopping operation ofthe first lamp and operating the second lamp in response to receipt ofthe fail signal.

[0014] According to another aspect of the invention, a method forproviding visual notification of required replacement of ananti-collision light prior to failure of the anti-collision light,comprises providing an anti-collision light including a lamp, operatingthe lamp at a first flash rate at a light intensity above apredetermined light intensity value, and operating the lamp at a secondflash rate distinguishable from the first rate when the light intensityof the lamp approaches the predetermined light intensity value.

[0015] According to get another aspect of the invention, a lamp fixturecomprises an annular reflector and first and second annular lampssurrounding the reflector, and the reflector having a reflector surfaceconfigured to reflect light outwardly from the lamp fixture from both ofthe lamps.

[0016] The foregoing and other features of the invention are hereinafterfully described and particularly pointed out in the claims, thefollowing description and the annexed drawings setting forth in detailone or more illustrative embodiments of the invention, such beingindicative, however, of but one or a few of the various ways in whichthe principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a perspective view of a light intensity monitoringsystem constructed in accordance with the present invention.

[0018]FIG. 2 is an exploded perspective view of the light of FIG. 1.

[0019]FIG. 3 is a cross-sectional view of the light of FIG. 1.

[0020]FIG. 4 is an exploded perspective view of the light fixtureassembly included in the light of FIG. 1.

[0021]FIGS. 5 and 6 are interrelated functional block diagrams of theelectrical circuitry used in the light of FIG. 1.

DETAILED DESCRIPTION

[0022] Referring now in detail to the drawings, and initially to FIGS.1-3, a light constructed in accordance with the present invention isgenerally indicated at reference numeral 10. The light 10 was developedfor use as an aircraft recognition/anti-collision light and is hereindescribed chiefly in this context. However, those skilled in the artwill appreciate that a light according to the invention will have otheruseful applications including but not limited to uses in other types ofvehicles, in industrial applications, etc. It should be appreciated thatsuch alternative applications are contemplated as falling within thescope of the present invention. It also should be appreciated thatreferences herein to top and bottom, upper and lower, etc., are made inrelation to the illustrated orientation of the light to describepositional relationships between components of the light and not by wayof limitation, unless so indicated. Also, the terms “recognition” and“anti-collision” are used interchangeably.

[0023] As shown in FIGS. 1-3, the anti-collision light 10 includes ahousing 12 composed of upper housing member or cover 14, a lower housingmember or case 16, and a mounting plate 18 disposed between the cover 14and case 16. The cover 14 is transparent and preferably has a Fresnellens 20 integrally formed therein. The cover, which may also be providedwith a conventional drain plug 22, is secured to the top side of themounting plate 18 by a hold-down ring or lens bezel 24. The case 16 isfastened to the underside of the mounting plate 18 by fasteners (notshown) or other suitable means. Together, the cover 14, case 16 andmounting plate 18 define an interior region 26 for containing theinternal components of the light 10, which internal components generallycomprise a flashtube fixture assembly 28, a fixture base 30 andelectrical circuit components 32 for supplying power to and controllingthe flashtube fixture 28.

[0024] As seen in FIG. 3, the flashtube fixture assembly 28 includes twoflashtubes 34 and 36 and a common spool-shaped reflector 38. Thereflector 38 includes upper and lower reflector half spool members 40and 42 that are axially aligned and coupled together. The reflector 38is coupled to the fixture base 30 which, in turn, is fastened to themounting plate 18.

[0025] The flashtubes 34 and 36, which are herein referred as a main orprimary flashtube and a spare or secondary flashtube 36, respectively,are conventional circular-shaped (annular) flashtubes that are disposedcircumferentially around the waist (smallest diameter portion) of thespool-shaped common reflector 38 in substantially parallel relation toone another. The main flashtube (or spare flashtube) 34 can be eitherthe upper or lower flashtube shown in the illustrated light. Theflashtubes 34, 36 preferably are supported in spaced apart parallelrelationship, such as by respective centering spacers 44.

[0026] With additional reference to FIG. 4, the centering spacers 44have central disk portions 46 from which support arms 48 radiate. Asshown, four circumferentially equally spaced apart support arms 48 maybe provided for each spacer. The radially outer ends 50 of the supportarms 48 are contoured to support the corresponding flashtube 34, 36 andeach arm 48 may have a hole 52 and slot 54 therein for receipt of a wire(not shown) wrapped around the flashtube 34, 36 to hold it to thesupport arm 48 and thus to the centering spacer 44. Each centeringspacer 44 is affixed to the narrower end of a corresponding one of theupper and lower reflector halves 40 and 42 by suitable fastening meanssuch as screws 60. Other, or alternative, types of spacers may beemployed to support and maintain a spaced relationship between the mainflashtube 34 and spare flashtube 36.

[0027] The upper and lower reflector halves 40 and 42 progressivelydecrease in diameter (width) going from their axially outer ends totheir axially inner ends that are butted together at the waist 66 of thehourglass shape reflector 38. Each reflector member 40, 42 has aninterior annular region (chamber) 68, 70 disposed between a radiallyouter wall 72, 74 and an interior center post 76, 78. The interiorannular chamber 68, 70 is closed at the axially inner end of thereflector member 40, 42 by an axial end wall 80, 82 while the other endof the reflector member 40, 42 has an opening 84, 86 through which atrigger inductor assembly 88, 90 (FIG. 4) can be inserted into theinterior region 68, 70. The trigger inductor assembly 88, 90 includes aPTFE inductor housing 96, 98 containing a trigger inductor 100, 102. Thetrigger inductor 100, 102 is electrically connected by leads (not shown)to terminal ends 104, 106 of the corresponding flashtube 34, 36. Theterminal end portions 104, 106 extend perpendicularly to the plane ofthe otherwise annular flashtubes 34, 36. The terminal end portions 104,106 extend through an opening 108 (only one of which is shown) in theradially outer wall 110, 112 of the reflector half 40, 42 and into theinterior region 68, 70. After the electrical connections have been made,preferably the terminal ends 104, 106 and trigger inductor assemblies88, 90 are potted into their respective interior region 68, 70 with asuitable potting compound.

[0028] Together each flashtube 34, 36, reflector half 40, 42 and triggerinductor assembly 88, 90 form a respective light module 114, 116. In theillustrated embodiment the light modules 114 and 116 are substantiallyidentical except for their electrical connections. The trigger inductormodule 90 and flashtube 36 of the lower light module 116 areelectrically connected to a printed circuit board 118 fixed to thebottom (axially outer) end of the reflector half 42. The bottom printedcircuit board 118 is provided with pins 120 to form a plug that mateswith a corresponding socket (not shown) in the fixture base 30.

[0029] The bottom printed circuit board 118 also has through pinsconnected to an upper printed circuit board 126 at the axially inner endof the lower light module 116. The upper printed circuit board 126 isprovided with pins 128 for mating with sockets provided on a printedcircuit board 132 fixed to the bottom (axially inner) end of the upperlight module 114. The sockets are electrically connected to the triggerinductor module 88 and flashtube 34, and any other supporting electricalcircuitry may be provided on a printed circuit board 134 fixed to thetop (axially outer) end of the upper light module 114.

[0030] With the foregoing preferred construction of the light fixture28, the light fixture 28 is assembled by plugging the upper and lowermodules 114, 116 together and the lower module 116 to the fixture base30. When thus assembled, the upper and lower light modules 114 and 116may be held securely together and to the fixture base 30 by a bolt (notshown) that extends through the center tube 76, 78 and has its lower endthreaded into the fixture base 30, such as into a nut fastener attachedto the underside 136 of the top wall 138 of the fixture base 30 or byany other suitable means.

[0031] In view of the foregoing, it can be seen that the modularconstruction of the light 10 facilitates replacement of a defectiveand/or worn out module 114, 116, as well as assembly of the lightfixture 28 in the first instance. Together, the joined upper and lowerlight modules 114, 116 form the reflector 38 that is shared by and thuscommon to the two flashtubes 34 and 36.

[0032] The reflector 38 has an outer annular concave reflective surface140 for reflecting light emitted by either one of the flashtubes 34, 36substantially radially (horizontally) outwardly to provide 360 degreehorizontally concentrated illumination. Preferably, the reflectivesurface 140 has upper and lower semi-parabolic shaped half surfaceportions 142 and 144 respectively formed on the upper and lowerreflector halves 40, 42. The focal points of the half portions 142, 144preferably are axially spaced apart such that the main flashtube 34 canbe positioned at one focal point and the spare flashtube 36 can bepositioned at the other focal point. Because of the annular nature ofthe reflector 38 and flashtubes 34, 36, the focal points are actuallyfocal lines with which the annular axes of the flashtubes 34, 36 arealigned. Most preferably, the semi-parabolic shaped half surfaceportions 142 and 144 each extend slightly beyond the center plane 146 ofthe respective parabola but not so far as to shade any of the reflectivesurface from light emitted from either flashtube 34, 36. Although thefocal points of the two half surface portions 142, 144 are spaced apart,they are sufficiently close to reflect and focus light emitted not onlyfrom the closest flashtube 34, 36 but also the furthest flashtube 34,36.

[0033] As will be appreciated, the light rays passing from a flashtube34, 36 to the nearest half surface portion 142, 144 of the reflector 38will be reflected so as to pass generally radially away from thereflector 38 to provide a horizontally concentrated light pattern.However, the light rays passing from a flashtube 34, 36 to the furthesthalf surface portion 142, 144 will be outwardly divergent from thehorizontal because the flashtube 34, 36 is oppositely spaced from thefocal point of such furthest half surface 142, 144. In thoseapplications where it is desirable to concentrate the light intensitywithin a specified angle from horizontal, such as 5 degrees for anaircraft recognition/anti-collision light, the cover 14 may be providedwith a Fresnel lens 20 (other suitable lens means or equivalent) toredirect the otherwise wayward rays into the desired horizontal window.

[0034] As seen in FIG. 3, the Fresnel lens 20 differs from the classicalFresnel lens by having two convex lens 148, 150 at the center withprisms 152, 154 above and below. The two convex lens 148, 150 arerespectively horizontally aligned with the flashtubes 34, 36. Inessence, each flashtube 34, 36 has associated therewith a parabolicreflector 142, 144 and Fresnel lens 20, except that the portion of eachsuch reflector 142, 144 and lens 20 that would interfere with the otheris removed and the two brought together along a center plane 146 equalspaced from the horizontal planes of the flashtubes 34, 36. Of course,other shaped reflector surfaces 140 and/or lens 20 may be employed toprovide other light patterns that may be desired for variousapplications.

[0035] As depicted in FIG. 2, the flashtube fixture 28 is provided witha light pipe (or other suitable light transmission means) 156 thatextends from an aperture 158 located in the wall 74 of the reflector 38and through an aperture 160 in the top wall 138 of the fixture base 30.Within the base 30, the light pipe 156 extends to a light detector 162,such as a photodiode, mounted on a printed circuit board constitutingone of the electrical circuit components 32 (FIG. 3). The light pipe 156attenuates and conveys light emitted by each flashtube 34, 36 to thephotodiode 162 for monitoring of light intensity in the hereinafterdescribed manner. The light intensity is monitored for the purpose ofcontrolling the operation of light in the following preferred manner.Preferably, the light pipe 156 functions to calibrate the lightattenuation as necessary for linear operation of the photodiode 162.

[0036] In operation, initially the main flashtube 34 is flashed at adesired frequency, such as at 42 flashes per minute which is within theflash rate range (40 to 100 fpm) mandated by FM regulations for aircraftoperation. The intensity of the flashtube 34 is monitored, preferablycontinuously, by the photodiode 162 and associated monitoring circuitry32. If the measured intensity is found not to be in compliance with apredetermined criteria, for example the measured intensity falls below aminimum specified light intensity, such as the 100 candela mandated byFAA regulations, power to the main flashtube 34 is boosted. This “powerboost” mode causes the main flashtube 34 to continue flashing above theFAA minimum effective intensity. Although this process can be repeatedmultiple times, preferably the power to the main flashtube 34 is boostedonly one time instead of incrementally.

[0037] During the main flashtube power boost mode, continuous monitoringof intensity of the main flashtube 34 continues until once again themeasured intensity is found not to be in compliance with a predeterminedcriteria, for example the measured intensity falls below a minimumspecified light intensity, such as the 100 candela mandated by FAAregulations. At this point, flashing of the main flashtube 34 is stoppedand in its place the spare flashtube 36 is flashed. Now it is theintensity of the spare flashtube 36 that is monitored. If the measuredintensity falls below the minimum specified light intensity threshold,power to the spare flashtube 36 is boosted. This “power boost” modecauses the spare flashtube 36 to continue flashing above the FAA minimumeffective intensity.

[0038] During the spare flashtube power boost mode, continuousmonitoring of intensity of the spare flashtube 36 continues until onceagain the measured intensity is found not to be in compliance with apredetermined criteria. At this point the spare flashtube 36 is causedto flash at a different rate to provide an indication that the light isclose to the end of its useful life. For example, the spare flashtube 36may be caused to flash at twice its normal frequency. Although changingthe flash rate provides an effective way of indicating a need to servicethe light, other indicating means may be employed such as providing anindicator light on the light unit, supplying a warning signal to theaircrafts control system for appropriate processing, such as display ona panel or screen in the cockpit, storing an indicator warning in memoryfor read-out by diagnostic equipment, etc.

[0039] The foregoing describes a preferred sequence of operation of themain and spare flashtubes 34 and 36. However, it should be appreciatedthat the sequence may be varied and/or portions thereof used inconjunction with a light having more or less flashtubes. For example,the power boost feature may be used with a single flashtube light toextend the useful life of the light. Also, the first and secondflashtubes 34, 36 may be sequentially cycled through their normal powermodes first, and then cycled through their power boost modes. Moreover,the first and second flashtubes 34, 36 may be alternately flashedaccording to some specified criteria, such as alternately for aspecified period or number of flashes. For example, the main flashtube34 may be flashed for 1000 flashes, then the spare tube for 1000flashes, then the main tube for 1000 flashes, and so on. Should eithertube's light output intensity fall below the minimum, it may be operatedin the power boost mode, no longer operated, or flashed at a differentrate to indicate a need for servicing.

[0040] The above described operation of the anti-collision light 10 iseffected by the electrical circuitry 32, the functional components ofwhich are illustrated by the functional block diagrams of FIGS. 5 and 6.The electrical circuitry 32 according to a preferred embodiment of theinvention generally comprises power supply circuitry generally indicatedat 164 in FIG. 5, and control and monitoring circuitry generallyindicated at 166 in FIG. 6, respectively.

[0041] Referring principally to FIG. 5, the power supply circuitry 164includes an EMI filter 168 to which input power is routed, such as 115VAC provided on an aircraft. The EMI filter 168 attenuates noisegenerated in a power supply 176 from being coupled on the aircraft powerline. The EMI filter 168 also suppresses noise on the power line thatcould affect the operation of the power supply. The EMI filter 168 maybe housed in an EMI can 172 provided in the housing 12 and equipped withan external power connector 174 as shown in FIG. 3.

[0042] The filtered power is used to power the circuits of the powersupply 176. The power supply 176 includes a transistor AC switch 177which controls the filtered AC power that is used for charging flashcapacitors 178. A preferred switch consists of two FET transistors in anAC bridge configuration that has slow turn-on to reduce in-rush currentwhen the flash capacitors 178 start to charge. The transistor on/offcontrol may be provided by an isolated switch control circuit 180 thattakes low voltage control signals that are referenced to ground andconverts them to control signal referenced to 115 VAC. A voltage doublercircuit 179 converts the 115 VAC to approximately +280 VDC and −280 VDCfor use as capacitor charging voltages. The voltage doubler 179 iscapable of producing 320 VDC from 115 VAC. The actual voltage developedis controlled by the power regulator 190 and can vary between 250 VDCand 295 VDC.

[0043] The flash capacitors 178 are used to supply the energy used bythe flashtube 34, 36. In a preferred embodiment, four capacitors may bearranged in two parallel sets that are connected in series. Theflashtube 34, 36, which may be a xenon gas flashtube, is connectedacross the series connected capacitors and provides a desired voltage ofabout 500 to 600 volts, for example, to the flashtube 34, 36.

[0044] More particularly, the anode and cathode of each flashtube 34, 36is connected to the outputs of the capacitors 178. In a preferredarrangement, the cathode of each tube 34, 36 is connected to the minuscapacitor through the secondary winding of the trigger inductor 100,102(transformer). The primary winding of the trigger inductor 100, 102 isconnected to a respective flashtube trigger generator circuit, therebeing a main flashtube trigger generator circuit 186 for the mainflashtube 34 and a spare flashtube trigger generator circuit 188 for thespare flashtube 36. When a trigger pulse, for example a −275 volt pulse,is applied to the primary winding of the trigger transformer, a highvoltage negative pulse, for example −5000 V to −7000 V, is developed bythe transformer secondary winding. This voltage causes the xenon gas inthe flashtube 34, 36 to change from an insulator to a low resistanceconductor, whereupon the flash capacitors 178 discharge through theflashtube 34, 36 creating a brilliant white flash of light. A groundedwire may be wrapped around the outside of the flashtube 34, 36 to helppropagated the ionization gas in the flashtube 34, 36 and provideshielding for EMI generated by the flashtube 34, 36 when it fires. Thisminimizes cross-talk between the main and spare flashtubes 34, 36. Also,this method of triggering the flashtubes 34, 36 provides several otheradvantages. In particular, it permits the flashtubes 34, 36 to bemounted in close proximity to one another in stacked relationship which,in turn, allows the common reflector 38 to be used for both flashtubes34, 36. As a consequence, the optical design of the reflector 38 andlens 20 is greatly simplified. Another advantage is that series triggercircuits provide trigger voltage isolation between flashtubes 34, 36 sothat trigger coupling between the closely spaced flashtubes 34, 36,which typically causes erratic flashing in parallel trigger circuits, isprevented. The series trigger circuit also provides electromagneticshielding for the flashtubes 34, 36 which reduces electromagneticinterference (EMI) that the flashtubes 34, 36 are exposed to duringinitial triggering. It also reduces the amount of EMI suppressionrequired to meet FAA imposed EMI requirements.

[0045] The charging of the flash capacitors 178 is controlled by a powerregulator 190. After a flashtube 34, 36 fires and the flash capacitors178 are discharged, the regulator 190 receives a timing signal from aflasher timer 192 to start charging the capacitors 178. The regulator190 supplies a signal to the isolated switch control 180 that is used toturn-on the transistor AC switch 179, starting the charging cycle. Afterthe capacitors 178 have been charged to the voltage needed to obtain therequired power, the power regulator 190 turns off the signal to theisolated switch control 180 which turns off the AC power to the flashcapacitors 178. As the capacitors 178 age and their capacitance changes,the power regulator 190 adjusts the capacitor charging voltage to keepthe power output constant, which output is a function of the flashcapacitor capacitance and the capacitor voltage. This keeps power at aminimum level and extends the life of the flashtube 34, 36. When theflashtube intensity decreases below the minimum threshold, an intensitymonitor power boost latch 194 (FIG. 6) sends a signal to the powerregulator 190 to increase the power to the flashtube 34, 36. This willincrease the intensity and provide additional operating time for theflashtube 34, 36 as was discussed above.

[0046] The regulator 190 preferably has associated therewith an overvoltage monitor 196 that measures the positive and negative flashtubevoltages. If the charging voltage increases above a specified amount,for example, plus or minus 300 VDC, the over voltage monitor 196overrides the power regulator 190 with a turn-off signal to the isolatedpower control circuit 180. This would occur, for example, if theflashtube 34, 36 does not fire. In such event, the power regulator 190would attempt to charge the already charged capacitors 178 and would, ifnot stopped by the over voltage monitor 196, overcharge the capacitors178, and this may reduce their useful life.

[0047] As further shown in FIGS. 5 and 6, the electrical circuitryincludes a sync circuit 198 that supplies a sync signal, for example a400 Hz signal, to the flasher timer 192. This signal is used to controlall timing functions in the power supply 176 via the flasher timer 192which generates timing signals required by the power regulator 190 andthe trigger generators 186, 188. The timer 192 also generates a timingsignal for control of an intensity monitor circuit 200 that is discussedbelow. The trigger generators 186, 188 are capable of producing aflashtube trigger at a normal rate of 42 flashes per minute for example,and at least the spare trigger generator 188 is capable of producing aflashtube trigger at a different rate such as twice the normal rate or adouble flash trigger signal.

[0048] The power for the flashtube triggers 186, 188 is provided by atrigger power circuit 202. The trigger power circuit 202 may be apositive voltage doubler for supplying 300 VDC to the flashtube triggergenerators 186, 188. Each flashtube generator 186, 188 produces, forexample, a −275 volt pulse that is connected to the trigger coil of thetrigger transformer 100, 102 for the flashtube 34, 36. The pulse may begenerated by a capacitor discharge SCR circuit that is controlled by thelamp intensity monitor trigger control circuit 204, 206. If theflashtube 34 fails to fire, the capacitor voltage will be at a steadyvalue, either low or high depending on the cause of the flash notfiring. A flash detector 207 monitors the charging and discharging ofthe flash capacitors 178. If they are at a steady voltage and not beingcharged and discharged for a predetermined time period, the flashdetector 207 generates a fail signal that is sent to a main flashtubefail latch 208 to initiate the switching to the spare flashtube 36.Similarly, the spare flashtube generator 188 produces, for example, a−275 volt pulse that is connected to the secondary trigger coil of thetrigger transformer 102 for the spare flashtube 36. The pulse may begenerated by a capacitor discharge SCR circuit that is controlled by aspare lamp intensity monitor trigger control circuit 206.

[0049] As further seen in FIG. 5, the power supply 176 further comprisesa low voltage power supply 209 for supplying low DC voltage to theflasher power supply circuit and intensity monitor circuit. The lowvoltage power supply 209 may include a transformer that steps the 115VAC down to the desired DC voltages such as ±10 VDC and ±5 VDC. Thetransformer may also have an isolated winding that provides power to theisolated switch control circuit 180.

[0050] Referring now principally to FIG. 6, the intensity monitor andcontrol circuit 166 includes a photodiode circuit 210 including thephotodiode 162 which as above noted continuously monitors the lightintensity of the operating flashtube 34, 36 via the light pipe 156. Thephotodiode circuit 210 provides an output signal to an integratorcircuit 212 that is proportional to the light intensity generated by thethen operating flashtube 34, 36. As is preferred, the photodiode 162 isselected to produce a response that approximates the response of thehuman eye and to quantify the light intensity in candela, a photometricmeasurement allowing the intensity to be compared to requirements forFAA approved intensity photometric test measurements. The photodiode 162should also be capable of providing a stable output over the fulloperating temperature range of the flashtubes 34, 36. If the output ofthe photodiode circuit 210 or alternative light sensor is temperaturesensitive, then temperature compensation could be provided to provide anormalized output. As is preferred, the photodiode 162 may be packagedin a metal hermetically sealed case with a glass window forenvironmental protection.

[0051] The integrator circuit 212 converts the measured light intensityprovided by the photodiode circuit 210 into an integrated output voltagewhich is a function of the light intensity of the flash emitted byflashtube 34, 36. Since the light intensity of the flashes typicallyvaries by a small amount, the light from multiple flashes is integratedto obtain an average intensity. Averaging the light intensity frommultiple flashes provides a more stable signal for the determination ofthe actual light intensity output and prevents a false lamp fail signalfrom being generated as a result of occasional sub-threshold flash. Eachtime the flashtube 34, 36 flashes, the integration output voltage willincrease by an amount proportional to the intensity of the flash. Thus,the voltage obtained at a particular time is equal to the total voltageof all the flashes measured up to that particular time. Thus, the outputsignal of the integrator 212 is a DC voltage proportional to the averageintensity of the light output. After a prescribed number of flashes havebeen integrated, the output of the integrator 212 is compared by anintensity comparator 214 against a reference value provided by areference voltage source 216 and then the integrator 212 is reset (tozero) by the intensity monitor counter 200 before measuring a nextseries of flashes.

[0052] The intensity comparator 214 monitors the output of theintegrator 212 and produces an output indicative of whether theintegrator 212 output satisfies or does not satisfy the comparisoncriteria. In the illustrated embodiment, the comparator 214 produces aGO or NOGO signal based on a comparison of the integrator 212 outputsignal to a reference voltage preferably supplied by the referencevoltage source 216 which may be a stable temperature compensated voltagecircuit. The reference voltage level may be set in relation to the FAA'sminimum effective light intensity requirement, for example to correspondto the FAA's minimum effective light intensity requirement or slightlyabove such minimum requirement. If the integrator 212 output voltage isless than the reference voltage, the comparator 214 outputs a NOGOsignal. If the integrator 212 output voltage is greater than thereference voltage, the comparator 214 outputs a GO signal.

[0053] Initially the integrator 212 output voltage will be below thecomparator reference voltage and the comparator 214 will output a NOGOsignal. As consecutive light flashes are measured, the integrated outputvoltage will gradually increase from zero volts to the final voltagemeasured for the prescribed number of flashes. When the integrator 212output voltage rises above the reference voltage, the comparator 214will output a GO signal. If the intensity of the flashtube 34, 36decreases below the minimum limit, the comparator output will stay in aNOGO state.

[0054] After a set of flashes have been measured, the state of thecomparator output is stored in an intensity status latch circuit 220which is controlled by the intensity monitor counter circuit 200. Theintensity monitor counter 200 is clocked by the flasher timer 192 andprovides timing signals not only for the intensity status latch 220, butalso for the integrator 212, a light warm-up inhibit latch 222 and anintensity integrator fail counter 226. At power turn-on the counter isset to zero by a power-on reset circuit 225 and synchronizes theoperation of the counter.

[0055] After the intensity monitor counter 200 counts the prescribednumber of flashes for a set of flashes to be integrated for comparisonto the reference value, the counter 200 sends a clock signal to theintensity status latch 220 to have it store the GO/NOGO state of theintensity comparator output. This occurs shortly before the counter 200resets the integrator 212, setting it to measure another set of flashes.The latch 220 then ignores the comparator output until the next set ofmultiple flashes is measured and another clock signal sent by thecounter 200 to the intensity status latch 220.

[0056] Preferably the intensity status latch 220 is inhibited fromoutputting a NOGO signal for a preset period of time after the thenactive flashtube 34, 36 has been turned on. This allows the flashtube34, 36 to warm up to its operating temperature. Under some lowtemperature conditions, the light intensity of the flashtube 34, 36 maybe below the required intensity in which case a NOGO signal would beoutputted by the comparator 214 and captured by the intensity statuslatch 220 when, after a warm-up period, the light intensity wouldotherwise rise above the required minimum. An inhibit signal may besupplied from latch 222 to the intensity status latch 220 for theprescribed period governed by the intensity monitor counter 200, thatis, the time period may be based on a number of flashes needed to bringthe flashtube 34, 36 up to its operating temperature.

[0057] The GO/NOGO status of the intensity status latch 220 is monitoredby an intensity integrator fail counter circuit 226. The intensityintegrator fail counter 226 prevents premature switching of the mainflashtube 34 to the spare flashtube 36 when the light intensity of themain flashtube 36 approaches the minimum light intensity. Since thedecrease in light intensity usually is gradual, light output mayintermittently fall below the specified minimum light intensity. Theintensity integrator fail counter 226, which is clocked by the intensitymonitor counter 200, monitors the intensity status latch 220 for apredetermined number of consecutive NOGO output signals corresponding toconsecutive multiple sets of flashes. If the prescribed number ofconsecutive measurements are NOGO, the intensity integrator fail counter226 provides a fail signal in the form of a power boost latch set signalto the power boost latch 194 which enables the power boost mode of thepower regulator 190. In response, the power regulator 190 increases thevoltage to which the flash capacitors 178 are charged. The increasedvoltage corresponds to an increase in the light intensity of the mainflashtube 34. This, in effect, extends the useful of the main flashtube34. Moreover, this extends the lifetime of the main flashtube 34 beyondthe life the main flashtube 34 would otherwise have had if operated atthe higher voltage, as the lifetime of a flashtube typically decreaseswith increasing operating voltage.

[0058] After the power to the main flashtube 34 is boosted, theintensity integrator fail counter 226 continues to monitor the GO/NOGOstatus of the intensity status latch 220. If several consecutivemeasurements are NOGO, the intensity fail counter 226 provides a mainlamp fail signal to a main lamp fail latch 208 for initiating switchingto the spare flashtube 36. The main lamp fail latch 208 provides aninhibit signal to the main lamp trigger control 204 and an enable signalto the spare lamp trigger control 206 (during operation of the mainflashtube 34 the main lamp fail latch 208 outputs an inhibit signal tothe spare lamp trigger 206 to prevent the spare flashtube 36 fromflashing). The main lamp fail latch 208 also provides a reset signal tothe power boost latch 194 which causes the power regulator 190 to chargethe flash capacitors 178 to the original or normal power settings. Thespare flashtube 36 will now be flashed in place of the main flashtube34.

[0059] During flashing of the spare flashtube 36, the intensityintegrator fail counter 226 continues to monitor the GO/NOGO status ofthe intensity status latch 220 and the output of the intensityintegrator fail counter 226 is sent to a spare lamp fail latch circuit228. If several consecutive measurements are NOGO, the intensityintegrator fail counter 226 provides a lamp fail signal to the powerboost latch 194 which enables the power boost mode of the powerregulator 190. In response, the power regulator 190 increases thevoltage to which the flash capacitors 178 are charged. The increasedvoltage corresponds to an increase in the light intensity of the spareflashtube 36. This, in effect, extends the useful life of the spareflashtube. Moreover, this extends the lifetime of the spare flashtubebeyond the life the spare flashtube would otherwise have had if operatedat the higher voltage.

[0060] After the power to the spare flashtube 36 is boosted, theintensity integrator fail counter 226 continues to monitor the GO/NOGOstatus of the intensity status latch 220. If several consecutivemeasurements are NOGO, the intensity fail counter 226 provides a sparelamp fail signal to the spare lamp fail latch 228 which sends a doubleflash enable signal to the spare lamp trigger 206. The spare flashtube36 is then double flashed to provide a visible indication to the aircrew and/or ground maintenance personnel that the intensity of the lightis near the FAA minimum level. In the preferred embodiment, the spareflashtube 36 flashes at 84 flashes per minute, which is twice the 42flashes per minute in normal operation. Preferably, during doubleflashing, every other flash is generated at reduced power to limit thetotal power to the flashtube to a level that will not cause theflashtube to overheat and burn- out. Notably, both the normal (42 FPM)and the double (84 FPM) flash rate fall within the FAA's acceptableflash rate range. The “double flash” rate alerts aircraft maintenancepersonnel that the light intensity of the anti-collision light 10 isnear the minimum required effective intensity and that servicing of theanti-collision light 10 is required. The spare flashtube 36 willcontinue to double flash until repaired or replaced. As is preferred,battery power is provided when the light 10 is turned off to retain thelow intensity status until power is reapplied.

[0061] After both lamps have reached their end-of-life, it may bedesirable to flash both lamps simultaneously to generate sufficientlight output from the light fixture. This may require some redundancysuch as two sets of flash capacitors.

[0062] An operating hours counter circuit 230 counts the number offlashes that have been accumulated by the flashtubes 34, 36. The counter230 is clocked by the flasher timer 192 and increments each time aflashtube 34, 36 fires. As is preferred, the counter 230 is powered frombattery power and retains its count when the light 10 is not powered. Ina preferred embodiment, the counter 230 is capable of recording about26,000 hours of operation (about 67 million flashes) and can only bereset during maintenance when the flashtubes 34, 36 are replaced.

[0063] Although the invention has been shown and described with respectto certain preferred embodiments, equivalent alterations andmodifications will occur to others skilled in the art upon reading andunderstanding this specification and the annexed drawings. In particularregard to the various functions performed by the above describedintegers (components, assemblies, devices, compositions, etc.), theterms (including a reference to a “means”) used to describe suchintegers are intended to correspond, unless otherwise indicated, to anyinteger which performs the specified function of the described integer(i.e., that is functionally equivalent), even though not structurallyequivalent to the disclosed structure which performs the function in theherein illustrated exemplary embodiment or embodiments of the invention.In addition, while a particular feature of the invention may have beendescribed above with respect to only one of several illustratedembodiments, such feature may be combined with one or more otherfeatures of the other embodiments, as may be desired and advantageousfor any given or particular application.

What is claimed is:
 1. A recognition light comprising: a reflectorhaving an axis and first and second annular semi-parabolic reflectivesurfaces which have respective focal points axially spaced apart fromone another; and first and second annular lamps respectively disposed atthe focal points.
 2. The recognition light of claim 1, comprising acontrol circuit for sequentially operating the first and second annularlamps.
 3. The recognition light of claim 1, comprising a coversurrounding the reflector and lamps, the cover including a lens forfocusing the light along a plane perpendicular to the axis of thereflector.
 4. The recognition light of claim 1, the lens having firstand second Fresnel lens portions each including a convex lens and aprism lens, the convex lenses being disposed adjacent one another andtransaxially aligned with the first and second lamps, respectively. 5.The recognition light of claim 1, wherein the semi-parabolic reflectivesurface comprises a half-parabolic reflective surface.
 6. A recognitionlight comprising: a parabolic reflector; first and second annular lampssurrounding the reflector; and a cover surrounding the reflector andlamps, the cover including a lens for focusing the light along a planeperpendicular to the axis of the reflector, the lens including first andsecond Fresnel lens portions each including a convex lens and a prismlens, the convex lenses being disposed adjacent one another andtransaxially aligned with the first and second lamps, respectively.
 7. Arecognition light comprising: first and second lamps; a light detectorpositioned to detect light emitted from at least one of the lamps; amonitor circuit connected to the light detector for providing a failsignal when a characteristic of the light output of at least one of thelamps does not satisfy a specified criteria; and a control circuitconnected to the monitor circuit and the first and second lamps forfirst activating the first lamp and then the second lamp in response toreceipt of the fail signal of the monitor circuit.
 8. The recognitionlight of claim 7, wherein the second lamp is operative to flash at adifferent rate than the first lamp.
 9. The recognition light of claim 7,further including a spool-shaped reflector, the first and second lampsbeing circumferentially disposed around the narrow portion of thespool-shaped reflector, the spool-shaped reflector being operative toreflect light emitted by either of the first or second lamps.
 10. Therecognition light of claim 9, wherein the first and second lamps aresubstantially circular in shape and have common centers.
 11. Therecognition light of claim 9 or 10, wherein the first lamp is spacedfrom the second lamp by one or more spacers.
 12. The recognition lightof claim 11, wherein the one or more spacers comprise cantileveredspacer bars projecting outwardly from the narrow portion of thespool-shaped reflector.
 13. The recognition light of claim 12, whereinthe spool-shaped reflector is formed from first and second axiallyaligned half portions, the first half portion comprising an upper rim ofthe spool-shaped reflector, the second half portion comprising a lowerrim of the spool-shaped reflector.
 14. The recognition light of claim 8,wherein the spool-shaped reflector is formed from first and secondaxially aligned half portions, the first half portion comprising anupper rim of the spool-shaped reflector, the second half portioncomprising a lower rim of the spool-shaped reflector.
 15. Therecognition light of claim 14, wherein the half portions form incross-section a substantially arc-shaped reflective surface operative toreflect light emitted by the first or second lamp substantially radiallyoutwardly from the axis of the spool-shaped reflector.
 16. Therecognition light of claim 15, wherein the half portions define areflective surface at least partially parabolic in shape.
 17. Therecognition light of claim 16, wherein the first and second lamps aredisposed at the focal points of the partially parabolic shaped portions.18. The recognition light of claim 17, wherein the partially parabolicshaped portions are greater in size than that of a half parabola. 19.The recognition light of claim 7, wherein the electrical controlcircuitry includes a voltage doubler for triggering the first and secondlamps.
 20. The recognition light of claim 19, wherein the voltagedoubler comprises a series trigger transformer comprising a firsttrigger coil and a second trigger coil, and wherein the second triggercoil is serially connected to the cathode input of the lamps viarespective flash capacitors.
 21. The recognition light of claim 20,wherein when a trigger pulse is applied to the first trigger coil, at orwithin a predetermined time thereafter the cathode of the first orsecond lamp is subjected to a negative voltage pulse, thereby causingthe first or second lamp to flash.
 22. A recognition light for anaircraft, comprising: a flashtube; a light detector positioned to detectlight emitted from the flashtube; a monitor circuit connected to thelight detector for measuring the intensity of the detected light andcomparing the measured intensity with a reference value corresponding toa predetermined light intensity level; and a control circuit connectedto the flashtube and monitor circuit for flashing the flashtube at afirst power level and then at an increased power level when the measuredintensity drops below the reference value, thereby to increase theintensity of the flashes emitted by the flashtube to above thepredetermined light intensity level.
 23. A method for increasing theuseful life of a recognition light of an aircraft, comprising: flashinga flashtube; monitoring the light output of the flashtube; comparing themeasured light output of the flashtube with a reference valuecorresponding to a predetermined light intensity value; increasing thepower delivered to the flashtube when the measured light output dropsbelow the reference value, thereby to increase the intensity of theflashes emitted by the flashtube to above the reference value.
 24. Themethod of claim 23, further comprising providing a second flashtubeoperative to flash at a rate different than that of the first flashtube.25. The method of claim 24, further comprising triggering the secondflashtube before the measured light output of the first flashtube fallsbelow the reference value.
 26. The method of claim 24, furthercomprising monitoring the light output of the second flashtube and, whenthe light output of the second flashtube approaches the reference value,triggering the second flashtube to flash at a rate different than thatwhich the first flashtube flashed.
 27. A method for monitoring theuseful life of an aircraft recognition light, comprising: flashing aflashtube; monitoring the light output of the flashtube with a lightdetector that converts the detected light output into an integratedoutput voltage corresponding to the light output of a plurality offlashes of the flashtube.
 28. The method of claim 27, further comprisingproviding an intensity comparator for comparing the integrated outputvoltage to a comparator reference voltage.
 29. The method of claim 28,further comprising comparing the integrated output voltage to thecomparator reference voltage and, if the integrated output voltage isless than the comparator reference voltage, transmitting a NOGOcondition signal, and, if the integrated output voltage is greater thanthe comparator reference voltage, transmitting a GO condition signal.30. The method of claim 29, further comprising storing the conditionsignal in an intensity status latch.
 31. The method of claim 30, furthercomprising temporarily inhibiting the intensity status latch fromproviding a NOGO condition signal for a predetermined amount of time oruntil the first flashtube is sufficiently warmed up to provide accuratemeasurements.
 32. The method of claim 30, further comprising providingan intensity integrator fail counter for monitoring the GO/NOGOcondition signal of the intensity status latch for a predeterminednumber of consecutive decreases and transmitting a boost signal or failsignal in response thereto.
 33. The method of claim 32, furthercomprising monitoring the GO/NOGO condition signal and, if thepredetermined number of consecutive NOGO measurements is attained,transmitting a boost signal for initiating an increase in powercorresponding to an increase in the light output of the first flashtube.34. The method of claim 33, further comprising providing a secondflashtube operative to flash at a rate different than that of the firstflashtube, and continuing monitoring the GO/NOGO condition signal of theintensity status latch and, if the predetermined number of NOGOmeasurements is attained, transmitting a fail signal for initiatingoperating the second flashtube at a rate substantially similar to therate of the first flashtube.
 35. The method of claim 34, furthercomprising using the intensity integrator fail counter for monitoringthe GO/NOGO condition signal associated with the second flashtube and,if the predetermined number of NOGO measurements is attained,transmitting a boost signal for initiating an increase in powercorresponding to an increase in the light output of the secondflashtube.
 36. The method of claim 35, further comprising continuingmonitoring the GO/NOGO condition signal associated with the secondflashtube and, if the predetermined number of NOGO measurements isattained, transmitting a fail signal for triggering the second flashtubeto flash at the different rate.
 37. A method for increasing the usefullife of a recognition light, comprising: providing first and secondlamps; operating the first lamp; monitoring a characteristic of thelight output of the first lamp and providing a fail signal when thecharacteristic of the light output of the first lamp does not satisfy aspecified criteria; and stopping operation of the first lamp andoperating the second lamp in response to receipt of the fail signal. 38.A method for providing visual notification of required replacement of ananti-collision light prior to failure of the anti-collision light,comprising: providing an anti-collision light including a lamp;operating the lamp at a first flash rate at a light intensity above apredetermined light intensity value; and operating the lamp at a secondflash rate distinguishable from the first rate when the light intensityof the lamp approaches the predetermined light intensity value.
 39. Alamp fixture comprising an annular reflector and first and secondannular lamps surrounding the reflector, and the reflector having areflector surface configured to reflect light outwardly from the lampfixture from both of the lamps.